Multiple West Nile virus infections in horses in the Netherlands

So far, four horses in South Holland, in the area between Rotterdam and The Hague, have been shown to have recently contracted a WNV infection. A recent infection has also been confirmed in a horse south of Nijmegen.

Several other horses are currently suspected of being infected with WNV. Diagnostic testing is needed to determine whether these horses have also contracted the virus.

In addition to infections in horses, West Nile virus has also been detected in a song thrush, mosquitoes and a Dutch blood donor.

Mosquito season in full swing

Last year (2025), West Nile virus was first detected in September in three horses in the Netherlands. The first infected horse of 2026 was identified in early August. More infections have now been confirmed this year than in 2025. The geographical area in which infections have been detected has also increased. As the mosquito season is still in full swing, more infections may be identified in the coming period.

Neurological signs in infected horses

The infected horses showed neurological signs, including ataxia and muscle tremors. In some cases, the animals also had a fever. Four of these horses are recovering from their symptoms. One horse was euthanised due to the severity of its clinical signs.

West Nile virus is notifiable

The West Nile virus is a zoonotic virus and a notifiable disease in horses and birds in the Netherlands. The confirmed cases have therefore been reported to the Netherlands Food and Consumer Product Safety Authority (NVWA), and official samples have been collected from the horses concerned.

Measures to protect horses against West Nile virus

West Nile virus is transmitted by mosquitoes, including the common house mosquito. Horse owners can reduce the risk of infection by taking measures to limit their horses’ exposure to mosquitoes. These include keeping horses indoors around dusk and removing standing water and other potential mosquito breeding sites.

Vaccination against West Nile virus is also available for horses. Please bear in mind that it takes several weeks (four to six) after vaccination for protection to develop.

Wageningen Bioveterinary Research and Royal GD organised a webinar on West Nile virus. The webinar is available to watch on the Royal GD website, where a Q&A with practical information is also available.